In a typical cellular network, user equipment (UEs) communicate via a Radio Access Network (RAN) which can be connected to one or more core networks. A UE is a mobile terminal by which a subscriber can access services offered by an operator's network. The UE may, for example, be communication devices such as mobile telephones, cellular telephones, laptops or tablet computers, sometimes referred to as surf plates, with wireless capability. The UE may be portable, pocket-storable, hand-held, computer-comprised, vehicle-mounted mobile devices or any other suitable devices enabled to communicate voice and/or data, via the radio access network, with another entity (e.g., another mobile station or a server such as a content providing server).
UEs are enabled to communicate wirelessly in the cellular network. As described herein, a UE may include a processor, a memory, a transceiver, an antenna, and any other suitable components. In particular embodiments, some or all of the functionality described in this disclosure as being provided by UEs, machine-type-communication (MTC) or machine-to-machine (M2M) devices, and/or any other types of wireless communication devices may be provided by the device processor executing instructions stored on a computer-readable medium, such as the memory of the UE. Alternative embodiments of the wireless communication device may include additional components that may be responsible for providing certain aspects of the device's functionality, including any of the functionality described below and/or any functionality necessary to support the solution described herein.
The cellular network covers a geographical area which is divided into cell areas. Each cell area is served by a base station, such as a Radio Base Station (RBS), which sometimes may be referred to as an “eNB”, “eNodeB”, “NodeB”, “B node”, or Base Transceiver Station (BTS), depending on the technology and terminology used. As described herein, such a base station includes a processor, a memory, a transceiver, an antenna, and any other suitable components. In particular embodiments, some or all of the functionality described herein as being provided by a base station, a node B, an enhanced node B, and/or any other type of network node may be provided by the node's processor executing instructions stored on a computer-readable medium, such as the node's memory. Alternative embodiments of the base station may include additional components responsible for providing additional functionality, including any of the functionality identified below and/or any functionality necessary to support the solution described herein.
FIG. 1 illustrates an example architecture of an LTE system. As shown in FIG. 1, the LTE architecture includes a plurality of radio access nodes 115 (which may be interchangeably referred to as eNBs) and a plurality of evolved packet core nodes 130 (which may be interchangeably referred to as MME/S-GW or core network nodes). In addition, FIG. 1 illustrates the logical interfaces between eNBs 115 and between eNB 115 and MME/S-GW 130. As shown in the example of FIG. 1, an S1 interface connects eNBs 115 to MME/S-GW 130, while an X2 interface connects peer eNBs 115. In some cases, an example network may include one or more instances of wireless communication devices (e.g., conventional UEs, MTC/M2M UEs) and one or more radio access nodes (e.g., eNodeBs or other base stations) capable of communicating with these wireless communication devices along with any additional elements suitable to support communication between wireless communication devices or between a wireless communication device and another communication device (such as a landline telephone).
FIG. 2 illustrates an example management system for the example LTE architecture of FIG. 1. The node elements (NE) 115, also referred to as eNBs, are managed by one or more domain managers (DM) 205, also referred to as the operation and support system (OSS). DMs 205 may further be managed by a network manager (NM) 210. In the example of FIG. 2, two NEs 115 are interfaced by an X2 interface, whereas the interface between two DMs 205 is referred to as Itf-P2P. DMs 205 and NM 210 are interfaced by an Itf-N interface.
The management system may configure NEs 115, as well as receive observations associated to features in NEs 115. For example, in some cases DMs 205 observe and configure NEs 115, while NM 210 observes and configures DMs 205, as well as NEs 115 via DMs 205.
By means of configuration via DMs 205, NM 210 and related interfaces, functions over the X2 and S1 interfaces can be carried out in a coordinated way throughout the RAN, eventually involving the core network (i.e., MME and S-GWs 130 described above in relation to FIG. 1).
Multimedia Broadcast Multicast Service (MBMS), an example of a broadcast service, is a point-to-multipoint interface specification for existing and upcoming 3GPP cellular networks. MBMS is designed to provide efficient delivery of broadcast and multicast services, both within a cell as well as within the core network. For broadcast transmission across multiple cells, MBMS defines transmission via single frequency network configurations, also known as MBMS single frequency network (MBSFN) operation. Target applications include, for example, mobile TV and radio broadcasting, as well as file delivery and emergency alerts.
MBMS was introduced in 2005 for different types of RAN (i.e., for Global System for Mobile Communications (GSM), for Enhanced Data Rates for GSM Evolution (EDGE) RAN (GERAN), and for Universal Terrestrial RAN (UTRAN) Rel-6) and in 2010 (for Evolved UTRAN (E-UTRAN) Rel-9) for more efficient distribution of identical services (i.e., services that are identical for several users.
For MBMS, two new logical channels were introduced: the Multicast Control Channel (MCCH) and the Multicast Traffic Channel (MTCH). The MCCH carries information about MBMS specific transport channel configurations, in E-UTRAN (also referred to as Long Term Evolution (LTE)) the Multicast Channel (MCH), and the corresponding MBMS services, which are mapped one to one to an MTCH.
The MCCH contains information for the UE to be able to read a specific MBMS service. Both MCCH and MTCH are mapped to one or more MCHs. Each MCH can be configured with an individual modulation and coding scheme (MCS), and is selected according to the requirements of the control channels or the MBMS services that it carries, respectively.
In E-UTRAN, SystemInformationBlockType13 (SIB13), which is cell specific, contains information about MCCH configuration and scheduling, such that the UE can find and read the MCCH.
For MBMS, broadcast services are generally offered within a large geographic area consisting of one or more cells. In order to exploit this, these cells apply MBSFN operation, which means that identical signals are transmitted on the same time-frequency radio resources from each cell, such that the received signal power in the terminal (i.e., UE) is increased. The cells that offer the same set of MBMS services and the same scheduling of MBMS service sessions belong to one MBSFN area. The cells within the same MBSFN area transmit all MCHs within this MBSFN area in MBSFN mode (i.e., the corresponding MCCH and all MTCHs). In order to achieve MBSFN operation, one requirement is that the cells that belong to the same MBSFN area be tightly synchronized (e.g., in the order of microseconds).
From a terminal (i.e., UE) perspective, all signals transmitted from the cells within the MBSFN area combine over the radio resulting in an improved signal to interference and noise ratio (SINR). To protect the MBSFN signals from interference from surrounding cells, MBSFN area reserved cells are typically deployed at MBSFN area borders. MBSFN area reserved cells, however, are allowed to transmit other services on the resources allocated for the MBSFN transmission, but only with restricted power to avoid an unacceptable SINR degradation of the MBSFN signal. As the reserved cells do not transmit the broadcast service, the base station controlling the reserved cell requires less transmit power, which supports the idea of power efficient radio networks.
FIG. 3 illustrates an example E-UTRAN MBMS architecture. As shown in the example of FIG. 3, the architecture includes eNB 115, Multi-Cell/Multicast Coordination Entity (MCE) 305, Mobile Management Entity 310, and MBMS Gateway (GW) 315.
Typically, MCE 305 semi-statically configures which cells belong to the MBSFN area, and actively participates in the MBSFN transmission and in the determination of which cells are configured as reserved cells. MCE 305 also determines the MCS based on Quality of Service (QoS) requirements. MBSFN area configurations and MBMS scheduling information is provided from MCE 305 to eNBs 115 via the M2 interface (3GPP TS 36.443). The M2 interface is an E-UTRAN internal control plane interface. MCE 305 communicates with MME 310 over the M3 interface. The M3 interface is a control plane interface between E-UTRAN and the Evolved Packet Core (EPC). eNB 115 communicates with MBMS GW 315 via the M1 interface, a user plane interface.
In order to verify the actual MBSFN signal reception and properly configure MBSFN areas (such as the MBSFN area size or a set of modulation and coding schemes appropriate for specific services), support of MBSFN UE measurements was introduced in 3GPP Rel-12 utilizing the 3GPP Minimization of Drive Test (MDT) functionality. This feature is also known as MBMS MDT.
In order to better support critical communications, there is a 3GPP work item on MBMS Enhancements (SP-140883). In the TR phase, possible improvements to allow establishment of MBMS bearers using target area information (e.g., a list of cell identifiers), as distinct from using an MBMS Service Area, were considered. One option is that the application server (e.g., the Group Communication Service Application Server (GCS AS)), sends a list of cell identifiers to the Broadcast-Multicast Service Centre (BM-SC), which forwards this information to MCE 305. Based on the cell identifiers, MCE 305 will determine the MBSFN areas that have to participate in the MBMS service transmission. The cell identities of all cells within these MBSFN areas may then be reported back to the GCS AS. If the application server determines that new cells are supposed to provide the MBMS service, it can first check the broadcasting cell list before it sends a new request to the BM-SC. This avoids unnecessary signaling between the AS and the BM-SC.
Self-Organizing Networks (SON) enhancements have been studied in order to provide new features in LTE networks, such as different services, various UE types and dynamic deployment changes made possible as a result of wider usage of Active Antenna Systems (AAS). AAS in mobile communications are based on a combination of one or more antenna elements. The elements can be combined in different ways to focus the antenna transmission and reception with directivity. The antenna can transmit and receive more energy in some directions than in others.
AAS reconfiguration, based for example on OAM control or on distributed eNB-based logic, may include automatic cell splitting/merging/shaping, possibly even reusing Physical Cell Identifiers (PCIs)/E-UTRAN Cell Global Identifiers (ECGI) between old and newly activated cells (albeit with solutions to avoid PCI/ECGI ambiguities), and dynamically activating/deactivating cells. eNBs 115 may exchange information about cell state changes through X2 signaling (i.e., eNB CONFIGURATION UPDATE message sent after the change is taken into operational use). However, cell configuration change notifications are not foreseen to be communicated to the core network.
Similarly, cell reconfigurations involving activation/deactivation of cells can be adopted for energy saving purposes. In this case, cells would be activated/deactivated depending on UE density and traffic load in the area and according to energy saving targets. Such energy saving triggered changes in cell configurations are also notified between radio nodes via common interfaces such as the X2 interface.
As described above, MBSFN areas are typically semi-statically configured by MCE 305, which can optionally be based on MBSFN measurements performed by the UE. Obtaining an optimal MCS for a given service in a specific MBSFN area is rather complex as it involves multiple cells with different coverage. In SON, the process of activating/deactivating cells is something kept among eNBs 115, so all cells that are supported by the eNB (a cell can be active or dormant) may be considered active to an external node (i.e., MCE 305 may not be aware of dormant cells).
MCE 305 typically selects the MCS based on the assumption that all cells within the MBSFN participate in the MBSFN transmission. Such an approach, however, suffers from certain deficiencies. For example, because dormant cells do not participate in the MBSFN transmission, this will degrade the MBSFN signal strength, which may result in poor user experience. Furthermore, if MBSFN measurements were configured, the resulting measurement reports may cause misconfiguration of the MBSFN area. As one example, this may happen if the MBSFN signal was measured when all cells were active, such that an MCS with higher transmit rate is selected (if the cells are deactivated, there will be a degradation of the MBSFN signal). As another example, this may happen if the MBSFN signal was measured when there were dormant cells, such that a more robust MCS is selected resulting in lower transmit rate (if the dormant cells are activated, this will typically result in waste of resources).